1. Field of the Invention
The present invention relates to a light control apparatus for a vehicle which automatically turns on or off a vehicle headlamp.
2. Description of the Prior Art
A conventional control apparatus is shown in FIG. 4. In FIG. 4, 1 is a battery, 2 is a main fuse, 3 is an ignition switch, 4 is a control unit, 5 is a light sensor, 6A and 6B are headlamps, 7A and 7B are small lamps, 8 is a headlamp driving relay, 9 is a small lamp driving relay, 10 is a lighting switch and 11 to 14 are fuses. The battery 1 supplies power to the control unit 4 through the ignition switch 3.
In the OFF mode of the lighting switch 10, (open circuit conditions of the terminals AUTO, SMALL, and HEAD) the terminals AUTO, SMALL and HEAD of the unit 4 are all opened. In selecting the terminal (mode) SMALL, the terminal SMALL of the unit 4 is closed (remaining terminals are opened). In selecting the mode HEAD, the terminals SMALL and HEAD of the unit 4 are closed (terminal AUTO is opened). In selecting the mode AUTO, only the terminal AUTO of the unit 4 is closed (remaining terminals are opened), and the headlamps 6A, 6B and the small lamps 7A, 7B are driven by the control unit 4 through a relay respectively. The light sensor 5 is connected to the unit 4 with three lines; namely a power source line, a sensor output line and a grounding (SG) line.
When the mode HEAD on the lighting switch 10 is selected, the terminals SMALL and HEAD of the control unit 4 are closed (grounded), both relays 8 and 9 are driven and the headlamps 6A, 6B and the small lamps 7A, 7B are turned on. When the mode SMALL is selected, the terminal SMALL of the unit 4 is closed, and the relay 9 is driven to turn on the small lamps 7A and 7B. And when the mode AUTO is selected, the terminal AUTO of the unit 4 is closed, and the headlamps 6A and 6B are turned on or off in accordance with the output of the light sensor 5 through the control of the unit 4.
In this way, by selecting the automatic mode of the lighting switch 10, turning on or off the headlamp is automatically controlled. However, the above configuration has the following disadvantages.
(1) Since the power source supply is from only one fused source, if one of the units of the system malfunctions, even if the main unit is properly operating, excessive current is generated, and when the fuse is melted, all the headlamps are turned off. This brings about a very dangerous condition for night driving.
(2) Since the power source supply is from only one cable and, further, a connector is used in connecting the units, a loose contact or a cable break affects the system control, and this reduces reliability.
(3) The headlamps are turned on or off through the output of light sensor 5; however, a connector is used in connecting the light sensor 5 with the control unit 4 and this causes the problem of reducing reliability due to the connector contacts.
(4) Unless the terminal AUTO is in a completely closed condition, from the structural state of the lighting switch 10, there is a possibility that a manual mode is generated and the headlamps are turned off. Most of the recent lighting switches are of the direct coupling type. Since each signal is distributed through the connector, if the terminal AUTO is connected only via the contact of the connector, the problem in reliability described in item (2) remains.
(5) Since the headlamps are driven by only one relay, improving the headlamp reliability is restricted by the reliability of one relay.
(6) In the case of the problem of microcomputer runaway, there is a possibility that the headlamps being lighted are suddenly turned off, and safety in driving can not be assured.